A fuel vapor processor that prevents fuel in an automobile engine fuel tank from escaping into the atmosphere is described for example in Tokko Hei 5-69987 published by the Japanese Patent Office in 1993.
In this processor, fuel vapor in the engine tank is adsorbed on active carbon in a canister when the engine has stopped, and the canister is brought into contact with an engine intake passage under predetermined engine running conditions via a purge passage where a purge cut valve and a purge control valve are installed. When the engine is running, the intake passage is at a negative pressure. Fuel vapor released from the active carbon in the canister by means of this negative pressure and atmospheric air introduced in the canister is supplied to the intake passage, and is then burnt in the engine.
In this type of fuel vapor processor, fuel vapor tends to liquefy in the purge passage, and to build up in the purge cut valve or purge control valve. This liquefied fuel may turn to a sticky gum that adheres to the valve seat of the valves so that the valves may no longer function properly.